Methanol and dimethylether are useful feedstocks for preparing olefins in so-called oxygenate-to-olefins processes or as feedstock for preparing gasoline in a so-called oxygenate-to-gasoline process. Such an oxygenate-to-olefins process can convert methanol and/or dimethylether over a catalyst to a product stream that is typically rich in lower olefins, including ethene, propene, as well as butenes, pentenes, hexenes, and also higher olefins and other hydrocarbons and some by-products. The oxygenate feedstock can be obtained from synthesis gas, also referred to as syngas.
WO-A-2006020083 describes a process wherein synthesis gas is converted in a first step to methanol and in a second step to dimethylether. Water-containing oxygenates are formed in both the first and second reaction steps of the known process. A water removal unit serves for separating residual oxygenate components such as residual dimethylether and residual methanol from the water received therein. Wastewater streams obtained in the known process are preferably directed to a water treatment facility.
The separation of water-containing minimum concentrations of methanol and dimethylether from the effluents of the reaction contributes significantly to the cost and overall complexity of the process. There exists a desire to obtain a more simple process.